This invention relates to optocouplers and more particularly to a method of manufacturing optocouplers wherein the electrical performance thereof is monitored and optimized prior to final assembly.
Optocouplers are electronic components which transmit electrical information, without electrical connection, between a light source (emitter) and a light detector (receiver). The light emitted can be either invisible (e.g., infrared), or can be light in the visible spectrum. An input signal to the optocoupler causes the light source to turn on. When this happens, the light detector senses the light from the source, and produces an input signal proportional thereto. In this manner, the output signal follows the input signal without the need for any direct electrical connection between the input and output of the optocoupler. The input is coupled to the output optically rather than electrically; hence, the name optocoupler.
In order for an optocoupler to operate properly, the light source and light detector must be oriented properly with respect to each other. If too little light reaches the detector, then device sensitivity suffers. If too much light reaches the dectector, then device speed suffers because saturation of the phototransitor on the detector reduces its switching speed.
In the prior art, optocouplers have been manufactured by gluing a carrier containing a separate light source or plurality of light sources together with a carrier containing a light detector or plurality of detectors. After the carrier containing light sources and detectors are permanently secured to one another, the optocoupler is tested to determine whether it meets the electrical specifications for which it was designed.
In manufacturing optocouplers as described above, there is no precise control over the final orientation of the light source and light detector with respect to one another. Furthermore, the electrical connections made to the light source and light detector are not available for testing purposes until after the manufacture of the optocoupler is complete. This is due to the fact that in assembling optocouplers, an element known as a lead frame is used to form the leads through which electrical connections to the complete optocoupler can be made. A lead frame comprises a plurality of individual lead members that are tied together in a metal frame. All of the leads are electrically shorted together when they are in the lead frame. Free ends of the lead members are connected through delicate wires to proper points on the semiconductor light source and detector. The lead members are severed from the rest of the lead frame, and hence from one another, during a final step in the optocoupler packaging process. Since the individual leads are electrically shorted together until this final step, it is impossible to electrically test the optocoupler at any time prior to this step.
Once the package has been assembled and severed from the lead frame, it is too late to make any adjustment to the oricntation between the light source and light detector.
It would be advantageous to provide a method for manufacturing optocouplers wherein the orientation between the light sourcc and light detector can be adjusted prior to final assembly of the package containing the light source and light detector. In this way, the electrical characteristics of the optocoupler could be optimized during a continuous, automated manufacturing process.